airbnb/caravel

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

import roundDecimal from './roundDecimal';

export const EARTH_CIRCUMFERENCE_KM = 40075.16;
export const MILES_PER_KM = 1.60934;

export function kmToPixels(kilometers, latitude, zoomLevel) {
  // Algorithm from: http://wiki.openstreetmap.org/wiki/Zoom_levels
  const latitudeRad = latitude * (Math.PI / 180);
  // Seems like the zoomLevel is off by one
  const kmPerPixel =
    (EARTH_CIRCUMFERENCE_KM * Math.cos(latitudeRad)) / 2 ** (zoomLevel + 9);

  return roundDecimal(kilometers / kmPerPixel, 2);
}